For example, the molten salt described in Patent Document 1 has a lower melting point than a conventional molten salt. Therefore, the molten salt disclosed in this document has been investigated for use in a molten salt battery containing sodium. For practical utilization of a molten salt battery, increasing the charge capacity is an issue. Increasing the thickness of a positive electrode layer may be a solution to increasing the charge capacity. However, a problem is that when the thickness of the positive electrode layer exceeds a predetermined value, the charge capacity does not increase even if the thickness of the positive electrode layer is increased beyond the predetermined value.